(1) Field of the Invention
The invention relates to an arrangement for restituting selection signals from a received isochronous signal, the binary signal elements A and Z of which represent the sampling values of the selection signals, the sampling values having been taken at sampling instants having a given position relative to the signal transitions in the selection signals, in which the isochronous signal is applied to a buffer receiving store.
The invention has application in the field of code and speed dependent multiplexing of start-stop telegraph signals and the associated selection signals, those of the CCITT B-type signaling in particular.
In this B-type signaling the selection signals may be constituted by dial pulses having a pulse duration-pulse interval ratio (nominal 60/40) located between given limits.
In accordance with CCITT recommendation R101 (reference D1) the dial pulses in the isochronous signal are represented by 2, 3 or 4 bits A and at least one bit Z. (A: start polarity; Z: stop polarity).
A (2) Description of the Prior Art
In accordance with reference D1 the dial pulses coming from the isochronous signal must be restituted in accordance with CCITT recommendation U2 (reference D2).
In accordance with this latter recommendation the characteristics of the dial pulses may vary between the limits indicated herebelow:
rate: 9-11 pulses/sec PA0 Z:A ratio 1:1,2 to 1:1,9 PA0 interval of polarity A:49.6-72.8 ms PA0 interval of polarity Z:31.4-50.5 ms
From this it can be derived that:
These requirements can be satisfied by restituting the intervals of stop polarity Z with a fixed duration of 41 ms and by restituting the intervals of start polarity A with a variable duration between upper and lower limits of 50 and 70 ms.
The variations in the received plurality of bits A and Z are then compensated for by having the duration of the intervals of stop polarity A vary. This will require the use of a buffer store storing the received bits A and Z, while the signals with measured intervals of polarity A and Z are applied to the output for the restituted signals.